If you solved this question yourself, then trust me you have a all very clear with the basics of this chapter.
If not then lets solve this together.
Speed with current is 20,
speed of the man + It is speed of the current
Speed in still water = 20 - 3 = 17
Now speed against the current will be
Speed of the man - speed of the current
= 17 - 3 = 14 kmph